# Domain of the relation

• Mar 28th 2012, 12:12 PM
Kibbygirl
Domain of the relation
My problem states:

Determine the domain of the relation, and determine whether the relation describes y as a function of x:

y=|x|
• Mar 28th 2012, 12:23 PM
Plato
Re: Domain of the relation
Quote:

Originally Posted by Kibbygirl
My problem states: Determine the domain of the relation, and determine whether the relation describes y as a function of x: y=|x|

A relation is a set of ordered pairs.
In this case: \$\displaystyle \{(x,|x|)\}\$.
The domain is the set of first terms. What is this set of values?

If no two pairs can have the same first term then the relation is a function on the domain.
Is this relation a function?
• Mar 28th 2012, 06:30 PM
Kibbygirl
Re: Domain of the relation
Would the domain just be x then? I'm not understanding what the domain would be when it is just listing a variable - though does the bars mean "absolute"?
• Mar 29th 2012, 02:07 AM
earboth
Re: Domain of the relation
Quote:

Originally Posted by Kibbygirl
Would the domain just be x then? I'm not understanding what the domain would be when it is just listing a variable - though does the bars mean "absolute"?

1. As Plato pointed out the domain is a set. Since there aren't any restrictions we can assume that x has real values. Therefore the domain is the set of all real numbers: \$\displaystyle \mathbb{R}\$

2. \$\displaystyle abs(a) = |a|\$